1. Field of the Invention
The present invention relates to a semiconductor memory device having a page mode, and more particularly, to a method for reading data in the page mode.
2. Description of the Related Art
When a conventional semiconductor device is operating in a page mode, a cell address is designated, and data are read out in parallel from a cell of a memory cell array which corresponds to the address designated, and are supplied to a plurality of sense amplifiers. By changing the page address, data can be read out sequentially from the sense amplifiers and supplied in sequence to an output terminal via an output buffer.
FIG. 1 is a chart showing the timing of a reading operation of a conventional mask ROM (Read Only Memory) in an 8-bit page mode. Of address signals A0-A19 shown in FIG. 1, signals A0-A2 are used as page address signals, and signals A3-A19 are used as cell address signals indicating address A of a memory cell storing the eight data to be read out from the memory cell array. Upon input of the address signals A0-A19, the eight data are read out in parallel from the cell, and are supplied to the sense amplifiers. One of the eight data read out is designated by the page address signals A0-A2, and is supplied to the output terminal via the output buffer. By changing the page address (A0-A2), the remaining seven data are sequentially selected and supplied to the output terminal via the output buffer. In the case where new eight data are read out from a cell of address B, the content of the address signals A0-A19 is changed, as a result of which the eight data are read out in parallel from the cell of address B and are supplied to the sense amplifiers. One of the eight data is designated by the page address signals A0-A2, and is output to the output terminal via the output buffer. By changing the page address (A0-A2), the remaining seven data are sequentially selected and supplied to the output terminal via the output buffer.
In the case of a data reading method such as that described above, output data Dout is in an unspecified state during the period of time (marked XXXX in FIG. 1) from a change in the cell address (A3-A19) to a change in the page address (A0-A2). In short, reading of data is not performed during this period, preventing high-speed reading in the page mode.
In the page mode of a conventional semiconductor device, as explained above, reading of data is not performed during the period of time from a change in the cell address to output of read-out data, preventing high-speed reading from being attained.